The present invention relates to apparatus for clamping a plurality of elements and, more particularly, to such apparatus as are used for clamping a plurality of electrodes in an electrical discharge machine used for simultaneously machining a plurality of small holes in a workpiece.
Electrical discharge machines have been used in the past to simultaneously machine a plurality of small holes in a wide variety of workpieces. These machines utilize a series of controlled electrical discharges to remove metal from the surface of the workpiece. More specifically, each of the discharges cause a minute amount of metal to rapidly heat up, melt and partially vaporize. The pressure of the metal vapor expels the liquid metal from the surface of the workpiece and into flowing dielectric fluid which carries the minute amount of metal away from the workpiece. The controlled electrical discharges occur at a rate or frequency, typically 15,000 to 30,000 per second, to continuously remove metal from the site. As metal is continuously removed, a depression is formed and the electrode used in generating the discharge is moved closer to the workpiece to maintain a selected discharge gap. In this manner then metal is removed from the site until the desired amount of metal is electrically machined away.
It is known in the art to employ a plurality of mutually insulated electrodes to simultaneously machine away metal at a number of closely proximate sites. This type of electrical discharge machine apparatus comprises a cluster, or plurality, of mutually insulated electrodes clamped onto and carried by a cartridge and selectively advanced as a group toward the workpiece. During the electrical discharge machining operation material is removed or eroded from the electrode as well as the workpiece. Erosion of the electrode tips during the machining operation may not be uniform amongst electrodes. Consequently, at the end of the machining operation, in order to achieve satisfactory operation during the next subsequent machining operation, the electrode tips must be placed in the same alignment as they exhibited at the start of the machining operation. Realignment of the electrode tips, or refeed as it is commonly known in the art, has been accomplished by releasing the clamp securing the electrodes to the cartridge, advancing selected electrodes toward the workpiece until the electrode tips are aligned in the desired relationship and reclamping the electrodes in the cartridge.
In the past, prior art apparatus for realigning or refeeding the electrode tips have met with generally successful results in realigning electrodes which lie generally parallel in the same plane. With the electrodes arranged to lie in the same plane, the clamps used to secure the electrodes to the cartridge may be very simply comprised of a pair of flat plate members or a pair of rollers between which the electrodes are gripped. However, prior art structures have not been completely successful in providing for realignment where the electrodes do not lie in the same plane but rather are disposed in a three dimensional array. The present invention addresses the problems posed by realignment of electrodes arranged in a three dimensional array.